Although the term "learning" is normally applied to the storage of complex percepts, such as the recognition of new objects or faces, there is increasing evidence that our perception of even simple stimulus attributes, such as the orientation or position of a line, is not fixed but can improve considerably with practice. These improvements have been termed perceptual learning to emphasize the similarities between these processes and classical forms of learning in other parts of the brain. This study examines learning in early levels of visual processing, utilizing the visual system to examine basic mechanisms of neuronal plasticity. A combination of approaches utilizing extracellular recording, optical imaging and pharmacologic manipulations will be used to examine perceptual learning in a visual discrimination task and the neuronal substrate by which This process takes place. Studies in somatosensory and auditory systems have shown that perceptual improvements in sensory discriminations are correlated with changes in neuronal response specificity at early levels of cortical processing. There is an increase in the amount of cortex which responds to the discrimination stimulus, which presumably leads to improved perceptual capabilities by allowing a larger number of neurons to participate in the task. We seek to observe analogous changes in the visual system by obtaining maps of the functional architecture of primary visual cortex before and after monkeys are trained on a visual discrimination for a period of several months. Through a subsequent series of pharmacologic manipulations in which we block various inputs to the region of cortex in which these changes occur, we hope to elucidate the patterns of neuronal connectivity which form the substrate for the perceptual improvements.